1. Field of the Invention
The present invention relates to the field of optical burst switched networks, and particularly to an QoS-oriented burstification method supporting various grades of burstification delay guarantee on the basis of delay requirement.
2. Description of Related Art
The ever-growing demand for Internet bandwidth and recent advances in optical Wavelength Division Multiplexing (WDM) technologies brings about fundamental changes in the design and implementation of the next generation optical Internet. Current applications of WDM mostly follow the circuit-switching paradigm by making relatively static utilization of individual WDM channels. As opposed to circuit switching, optical packet switching technologies enable fine-grained on-demand channel allocation and have been envisioned as an ultimate networking solution of IP over WDM. Nevertheless, optical packet switching currently faces some technological limitations, such as the lack of optical buffer, contention resolution, and switching overhead. Optical burst switching (OBS), as a result, has been emerged as a prominent coarse-grained optical packet switching solution attempting to combine the best of both optical circuit and packet switching while circumventing their limitations. Such technology, on the other hand, raises significant Quality-of-Service (QoS) challenges that need to be examined from both technical and economic perspectives.
Pertaining to OBS, as shown in FIG. 1, each ingress router 11 is required to perform the burstification process, namely the assembly of incoming IP packets destined for the same egress router 12 into bursts. Bursts are disassembled into packets at the egress router 12. In the system, assuming the propagation delay is negligible, a packet from ingress router to egress router incurs an end-to-end delay comprising the burstification delay and the inter-nodal switching delay. Therefore, it is desired to provide a QoS-oriented burstification mechanism offering different classes of burstification-delay guarantees for packets.
Assuming First Come First Service (FCFS), there are two basic burstification schemes: Burst Assembly Time (BAT)-based, and Fixed Burst Size (FBS)-based. In the BAT-based scheme, packets arrive during a BAT are assembled into a burst. The scheme assures bounded burstification delay but may result in lower throughput owing to bursts with few packets possibly generated. In contrast, the FBS-based scheme guarantees the generation of fixed-size bursts, however, at the expense of an increase in burstification delay.
With the delay-QoS taken into account, existing scheduling disciplines have placed emphasis on the design of scalable packet schedulers achieving fairness and delay QoS guarantee while retaining manageable complexity. In these schemes, all packets follow the exact departure order that is computed according to deadlines and virtual finishing times that are associated with packets. For burstification process, considering hundred or thousand of packets in a burst, the exact order of packets within a burst is completely insignificant. The above schemes are therefore economically unviable with respect to burstification process.